Antibody level dynamics until after the third dose of COVID-19 vaccination

Fig. 1. The antibody titers of people in the younger population were significantly higher than those in the elderly population. Serum specimens were collected from 105 volunteers who received the BNT162b2 vaccine (Pfizer-BioNTech) against SARS-CoV-2. The antibody titers were measured in sera 7–14 days after the second vaccination. Dot plots show the antibody titers and mean values of the age groups. A significant difference in the antibody titers was observed between people in their 20s and other age groups (a). The antibody titers in volunteers aged <60 years were significantly higher than those in volunteers aged ≥60 years (b). There were no significant differences in the antibody titers between male and female (c). *p < 0.01. **p < 0.05.

Fig. 2. The antibody titers after the third dose returned to levels after the second vaccination. The antibody titers of 44 healthcare workers were measured at nine time-points. The antibody titers decreased approximately eight months after the second vaccination (p < 0.001), but recovered after the third vaccination to the level after the second vaccination (p > 0.9); *p < 0.01.

Fig. 3. Neutralizing activities were measured before and after the second vaccination. Neutralizing activities of 44 healthcare workers were measured at four time points: just before the second dose, a week, three weeks and nine weeks after the second vaccination; *p < 0.01.

Fig. 4. Correlation between the antibody titers and neutralizing activity. The relationship between the antibody titer and neutralizing activity was analyzed at four time points: immediately before the second dose (a), a week (b), three weeks (c) and nine weeks (d) after the second vaccination. The correlation coefficients (r) and p-value were determined. An inhibition rate of >50% was considered positive.